Ethanol and a rapid-acting antidepressant produce overlapping changes in exon expression in the synaptic transcriptome

It is not just about transcription: involvement of brain RNA splicing in substance use disorders

Alternative splicing is a co-transcriptional process that significantly contributes to the molecular landscape of the cell. It plays a multifaceted role in shaping gene transcription, protein diversity, and functional adaptability in response to environmental cues. Recent studies demonstrate that drugs of abuse have a profound impact on alternative splicing patterns within different brain regions. Drugs like alcohol and cocaine modify the expression of genes responsible for encoding splicing factors, thereby influencing alternative splicing of crucial genes involved in neurotransmission, neurogenesis, and neuroinflammation. Notable examples of these alterations include alcohol-induced changes in splicing factors such as HSPA6 and PCBP1, as well as cocaine's impact on PTBP1 and SRSF11. Beyond the immediate effects of drug exposure, recent research has shed light on the role of alternative splicing in contributing to the risk of substance use disorders (SUDs). This is exemplified by exon skipping events in key genes like ELOVL7, which can elevate the risk of alcohol use disorder. Lastly, drugs of abuse can induce splicing alterations through epigenetic modifications. For example, cocaine exposure leads to alterations in levels of trimethylated lysine 36 of histone H3, which exhibits a robust association with alternative splicing and serves as a reliable predictor for exon exclusion. In summary, alternative splicing has emerged as a critical player in the complex interplay between drugs of abuse and the brain, offering insights into the molecular underpinnings of SUDs.

A paradoxical switch: the implications of excitatory GABAergic signaling in neurological disorders

Gamma-aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system. In the mature brain, inhibitory GABAergic signaling is critical in maintaining neuronal homeostasis and vital human behaviors such as cognition, emotion, and motivation. While classically known to inhibit neuronal function under physiological conditions, previous research indicates a paradoxical switch from inhibitory to excitatory GABAergic signaling that is implicated in several neurological disorders. Various mechanisms have been proposed to contribute to the excitatory switch such as chloride ion dyshomeostasis, alterations in inhibitory receptor expression, and modifications in GABAergic synaptic plasticity. Of note, the hypothesized mechanisms underlying excitatory GABAergic signaling are highlighted in a number of neurodevelopmental, substance use, stress, and neurodegenerative disorders. Herein, we present an updated review discussing the presence of excitatory GABAergic signaling in various neurological disorders, and their potential contributions towards disease pathology.

Cherry leaf decoction inhibits NMDAR expression and thereby ameliorates CUMS- induced depression-like behaviors through downregulation of α2δ-1

Depression is a complex and prevalent mental illness. Cherry leaf is a traditional Chinese herbal medicine, which has confirmed to exert a certain antidepressant effect, but its potential neural regulation mechanism is not clear. This paper aims to investigate the improved action of cherry leaf decoction (CLD) on chronic unpredictable mild stress (CUMS) rats and its potential neural regulation mechanism by verifying the role and function of NMDAR regulatory target α2δ-1 in depression due to CUMS. Male SD rats were subjected to random stressors persisting for 5 weeks to establish the CUMS depression rat model. CLD could effectively alleviate depression-like behaviors of CUMS rats in behavioral tests including sucrose preference test, forced swimming test, tail suspension test and open field test. After the administration of the CLD, the expression of corticotropic-releasing hormone (CRH) in the hypothalamus was inhibited. Moreover, the levels of CRH, adrenal cortical hormone (ACTH) and corticosterone (CORT) in serum also decreased significantly. CUMS upregulated the expressions of α2δ-1, N-methyl-d-aspartate receptor 1 (NR1), NR2A and NR2B, and enhanced the binding ability to of α2δ-1 and NR1, which were reversed by CLD. The results demonstrated that CLD could ameliorate depression-like behaviors due to CUMS, which was related to the fact that CLD down-regulated α2δ-1 level and interfered with α2δ-1 binding to NR1, thereby reducing NMDAR expression and ultimately inhibiting HPA axis activity.

Conserved role for PCBP1 in altered RNA splicing in the hippocampus after chronic alcohol exposure

We previously discovered using transcriptomics that rats undergoing withdrawal after chronic ethanol exposure had increased expression of several genes encoding RNA splicing factors in the hippocampus. Here, we examined RNA splicing in the rat hippocampus during withdrawal from chronic ethanol exposure and in postmortem hippocampus of human subjects diagnosed with alcohol use disorder (AUD). We found that expression of the gene encoding the splicing factor, poly r(C) binding protein 1 (PCBP1), was elevated in the hippocampus of rats during withdrawal after chronic ethanol exposure and AUD subjects. We next analyzed the rat RNA-Seq data for differentially expressed (DE) exon junctions. One gene, Hapln2, had increased usage of a novel 3' splice site in exon 4 during withdrawal. This splice site was conserved in human HAPLN2 and was used more frequently in the hippocampus of AUD compared to control subjects. To establish a functional role for PCBP1 in HAPLN2 splicing, we performed RNA immunoprecipitation (RIP) with a PCBP1 antibody in rat and human hippocampus, which showed enriched PCBP1 association near the HAPLN2 exon 4 3' splice site in the hippocampus of rats during ethanol withdrawal and AUD subjects. Our results indicate a conserved role for the splicing factor PCBP1 in aberrant splicing of HAPLN2 after chronic ethanol exposure. As the HAPLN2 gene encodes an extracellular matrix protein involved in nerve conduction velocity, use of this alternative splice site is predicted to result in loss of protein function that could negatively impact hippocampal function in AUD.

Alcohol and the brain: from genes to circuits

Alcohol use produces wide-ranging and diverse effects on the central nervous system. It influences intracellular signaling mechanisms, leading to changes in gene expression, chromatin remodeling, and translation. As a result of these molecular alterations, alcohol affects the activity of neuronal circuits. Together, these mechanisms produce long-lasting cellular adaptations in the brain that in turn can drive the development and maintenance of alcohol use disorder (AUD). We provide an update on alcohol research, focusing on multiple levels of alcohol-induced adaptations, from intracellular changes to changes in neural circuits. A better understanding of how alcohol affects these diverse and interlinked mechanisms may lead to the identification of novel therapeutic targets and to the development of much-needed novel and efficacious treatment options.

Transcriptomics identifies STAT3 as a key regulator of hippocampal gene expression and anhedonia during withdrawal from chronic alcohol exposure

Alcohol use disorder (AUD) is highly comorbid with depression. Withdrawal from chronic alcohol drinking results in depression and understanding brain molecular mechanisms that drive withdrawal-related depression is important for finding new drug targets to treat these comorbid conditions. Here, we performed RNA sequencing of the rat hippocampus during withdrawal from chronic alcohol drinking to discover key signaling pathways involved in alcohol withdrawal-related depressive-like behavior. Data were analyzed by weighted gene co-expression network analysis to identify several modules of co-expressed genes that could have a common underlying regulatory mechanism. One of the hub, or highly interconnected, genes in module 1 that increased during alcohol withdrawal was the transcription factor, signal transducer and activator of transcription 3 (Stat3), a known regulator of immune gene expression. Total and phosphorylated (p)STAT3 protein levels were also increased in the hippocampus during withdrawal after chronic alcohol exposure. Further, pSTAT3 binding was enriched at the module 1 genes Gfap, Tnfrsf1a, and Socs3 during alcohol withdrawal. Notably, pSTAT3 and its target genes were elevated in the postmortem hippocampus of human subjects with AUD when compared with control subjects. To determine the behavioral relevance of STAT3 activation during alcohol withdrawal, we treated rats with the STAT3 inhibitor stattic and tested for sucrose preference as a measure of anhedonia. STAT3 inhibition alleviated alcohol withdrawal-induced anhedonia. These results demonstrate activation of STAT3 signaling in the hippocampus during alcohol withdrawal in rats and in human AUD subjects, and suggest that STAT3 could be a therapeutic target for reducing comorbid AUD and depression.

Chronic repeated predatory stress induces resistance to quinine adulteration of ethanol in male mice

BACKGROUND

Trauma related psychiatric disorders, such as posttraumatic stress disorder (PTSD), and alcohol use disorder (AUD) are highly comorbid illnesses that separately present an opposing, sex-specific pattern, with increased prevalence of PTSD in females and increased prevalence of AUD diagnoses in males. Likewise, PTSD is a risk factor in the development of AUD, with conflicting data on the impact of sex in the comorbid development of both disorders. Because the likelihood of experiencing more than one traumatic event is high, we aim to utilize chronic repeated predatory stress (CRPS) to query the extent to which sex interacts with CRPS to influence alcohol consumption, or cessation of consumption.

METHODS

Male (n = 16) and female (n = 15) C57BL/6 J mice underwent CRPS or daily handling for two weeks during adolescence (P35-P49) and two weeks during adulthood (P65-P79). Following the conclusion of two rounds of repeated stress, behavior was assessed in the open field. Mice subsequently underwent a two-bottle choice intermittent ethanol access (IEA) assessment (P90-131) with the options of 20 % ethanol or water. After establishing drinking behavior, increasing concentrations of quinine were added to the ethanol to assess the drinking response to adulteration of the alcohol.

RESULTS

CRPS increased fecal corticosterone concentrations and anxiety-like behaviors in the open field in both male and female mice as compared to control mice that had not been exposed to CRPS. Consistent with previous reports, we observed a sex difference in alcohol consumption such that females consumed more ethanol per gram of body mass than males. In addition, CRPS reduced alcohol aversion in male mice such that higher concentrations of quinine were necessary to reduce alcohol intake as compared to control mice. CRPS did not alter alcohol-related behaviors in female mice.

CONCLUSION

Collectively, we demonstrate that repeated CRPS can induce anxiety-like behavior in both sexes but selectively influences the response to ethanol adulteration in males.